1. Field of the Invention
The invention relates to a telescopic arm for carrying out or controlling a manipulation wherein an arm can be used on the master side or slave side of a master-slave telescopic telemanipulator and can also be used for forming the arm of a robot.
2. Discussion of the Background
FR-A-2 497 138 discloses a telescopic manipulator arm comprising at least two segments located on a common axis. The end segment comprises a tubular body carrying a toggle or knuckle joint at its end, as well as an intermediate part in which the tubular body can rotate. The segment adjacent to the end segment comprises a larger diameter tubular body in which slides the intermediate part.
As a function of whether it is a master arm or a slave arm, the toggle or knuckle joint carries a control handle or a tool, such as a gripper. The toggle joint enables the handle or tool to have two degrees of freedom respectively corresponding to an orientation movement (rotation of the handle or tool about its own axis) and an elevation movement (pivoting of the handle or tool about an axis orthogonal to its own axis and to the axis of the arm). A tool actuating movement (gripper tightening) is also transmitted across the toggle joint.
In FR-A-2 497 138, these three movements are transmitted across the end segment of the arm by three shafts arranged coaxially in accordance with the arm axis.
In the segment adjacent to the end segment, the transmission of the three movements of the toggle joint is ensured by square section shafts, whereof one is arranged along the axis of the arm. The two other shafts, as well as another square section shaft used for controlling the rotation of the tubular body of the end segment (azimuth movement) are arranged parallel to the axis of the arm and are equidistant thereof, in the annular space defined between the tubular bodies of the two segments.
The square section shaft arranged along the axis of the arm is rotatable with the central shaft of the lower segment as a result of four rollers mounted at the upper end of the central shaft, so as to be able to roll on the faces of the square section shaft parallel to the arm axis.
Each of the other square section shafts is integral in rotation with a pinion supported in a rotary manner by the intermediate part. To this end, a cylindrical sleeve joined to the pinion also carries four rollers able to roll on the faces of the corresponding shaft, which traverses said sleeve. All these pinions are identical and engage on identical toothed gears fixed to the upper end of two other concentric tubes of the end segment, as well as to the upper end of the tubular body of said same segment. Finally, the axial displacement of the intermediate part in the segment adjacent to the end segment is ensured by a chain and toothed gear system.
The arrangement of the movement transmission shafts in the telescopic manipulation arm described in FR-A-2 497 138 makes it possible to perform the azimuth movement without bringing about any twisting of the shafts.
However, the use of several concentric shafts in the internal tubular body leads to said shafts having different weights and to their being supported at the lower end by bearings having different diameters. The drive friction of the bearings and the inertia consequently differ between individual shafts, which leads to differences in the transmitted torques and in the distribution of the forces.
In practice, these differences lead to an asymmetry in the transmission of the orientation and elevation movements of the handle and tool, because these movements require the combined rotation of two of the concentric shafts. They also appear on carrying out an azimuth movement, because the latter requires the rotation of the other shafts.